The present invention relates to hybrid construction equipment.
As for conventional construction equipment, a hydraulic drive type is mainstream. For example, a hydraulic shovel performs driving of a working machine, revolving of an upper revolving superstructure and traveling of a lower traveling unit with a hydraulic actuator (for example, a hydraulic cylinder, a hydraulic motor and the like). An operation is carried out by controlling pressure oil discharged from a hydraulic pump with an engine as a driving source and supplied to the hydraulic actuator as described above.
Operations of the hydraulic shovel include not only operations always requiring 100% of a capacity of an engine, but also many operations that only require, for example, 90% or 80% of its capacity. Specifically, as shown in an engine torque characteristic diagram in FIG. 3, in regard to a point PH of xe2x80x9ca heavy load modexe2x80x9d in which a heavy load operation with 100% of its output is performed, operation modes such as a point PS of xe2x80x9can ordinary load modexe2x80x9d in which an ordinary load operation is performed, and a point PL of xe2x80x9ca light load modexe2x80x9d in which a light load operation is performed are set. At each of the points PH, PS and PL, an equal horsepower control is performed so that absorption torque of a hydraulic pump matches with output torque of the engine, whereby the output of the engine is effectively utilized to improve fuel economy. Here, xe2x80x9cequal horsepower control for matchingxe2x80x9d means controlling the discharge amount of the hydraulic pump according to a PQ curve (an equal horsepower curve) so as to be able to obtain the absorption torque at the matching point. Further, the absorption torque of the hydraulic pump means torque required of the engine by the hydraulic pump to drive a hydraulic actuator.
In the above-described hydraulic shovel, mounted is an engine having output power corresponding to the maximum required horsepower when a vehicle performs operations, that is, an engine with a rated output point PH of the engine torque curve corresponding onto a maximum required horsepower line L shown in FIG. 3.
FIG. 4 is a graph showing a transition of absorption horsepower of the hydraulic pump in one cycle when xe2x80x9can excavating and loading operationxe2x80x9d in which excavated earth and sand are rotated and loaded into a damp vehicle is carried out in xe2x80x9cthe ordinary load modexe2x80x9d in which matching is achieved with 90% of rated output power of the engine. Load change of the hydraulic shovel is very sharp as compared with a passenger car and the like. However, as shown in FIG. 4, there is an allowance in the engine horsepower, and an average load rate with respect to the maximum horsepower of the engine in one cycle is about 80%, and the average load rate of the engine when measured with a day""s operation including traveling, waiting for damp vehicles and the like is about 60%. When the operation by xe2x80x9cthe heavy load modexe2x80x9d is performed, the average load rate does not become 100% because of a load change. Specifically, in a hydraulic shovel equipped with the engine having output power corresponding to the maximum required horsepower, the output power that the engine can produce cannot be effectively used.
As an art of eliminating the disadvantage, so-called hybrid construction equipment disclosed in, for example, Japanese Patent Laid-open No. 10-103112, which includes an engine, a generator driven by the engine, a battery for charging electric power generated thereby, and an electric motor driven by the electric power of this battery, is proposed. Using FIG. 5, a hybrid hydraulic shovel in the above-described Japanese Patent Laid-open No. 10-103112 will be explained.
Pressure oil discharged from a variable displacement type of hydraulic pump 52 driven by an engine 51 is supplied to a hydraulic cylinder 54a for driving a working machine and a hydraulic motor 54b for driving to travel, via a control valve 53. Pressure oil of an accumulator 56 held at fixed or higher pressure by pressure accumulation aiding means 55 is supplied to a hydraulic pump motor 58 for revolution via the control valve 57. As a result, the hydraulic cylinder 54a, the hydraulic motor 54b and the hydraulic pump motor 58 are driven, which makes it possible to drive the working machine, make a lower traveling unit travel, and revolve an upper revolving superstructure. When revolution is braked, the hydraulic pump motor 58 is switched into a pump operation, and following the rotation of the hydraulic pump motor 58, inertia energy is regenerated in the accumulator 56 as pressure energy.
The hydraulic pump 52 is equipped with a first electric motor 60 also serving as a generator, for which a controller 61 performs a switching control between a generating operation and an assisting operation and a torque control in each of them. Similarly, the hydraulic pump motor 58 is equipped with a second electric motor 62 also serving as a generator, for which a revolution controller 63 performs a switching control between a generating operation and an assisting operation and a torque control in each of them. A battery 64 is connected to the controller 61 and the revolution controller 63, and it accumulates electric energy obtained from the generating operations of the first and second electric motors 60 and 62 and discharges electric energy necessary for the assisting operations of the first and second electric motors 60 and 62.
The engine 51 the speed of which is governed by a governor 51a normally drives at a fixed engine speed. When an operation load is small, and absorption torque of the hydraulic pump 52 is smaller than output torque of the engine 51, the controller 61 switches the first electric motor 60 into a generating operation, performs a torque control of the first electric motor 60 so as to generate electric power by surplus torque, and charges electric energy generated from the surplus torque in the battery 64. When an operation load is large, and absorption torque of the hydraulic pump 52 is larger than output torque of the engine 51, the controller 61 switches the first electric motor 60 into an assisting operation, and performs a torque control of the first electric motor 60 so as to generate an amount of shortage of torque from discharge energy from the battery 64.
Based on a command value by a revolution operating lever 65 and a detection value by a rotation sensor 66, the revolution controller 63 performs (1) a torque control of the second electric motor 62 so as to carry out an assisting operation for speeding-up rotation during a motor operation of the hydraulic pump motor 58, or (2) a torque control of a generating operation of the second electric motor 62 so as to convert inertia energy exceeding a capacity of the accumulator 56 and regenerate it during a pump operation of the hydraulic pump motor 58.
According to the above-described constitution, power generation is carried out by surplus torque of the engine 51 when an operation load is small, thus making it possible to effectively use the engine 51, and energy regeneration is carried out at the time of braking revolution. When the operation load is large, absorption torque of the hydraulic pump 52 is increased by the assisting operation by discharge from the battery 64, and therefore an operation can be carried out with larger absorption torque than the maximum generation torque of the engine 51. Specifically, the engine 51 can be effectively used while energy conservation is achieved.
However, in the art disclosed in the above-described Laid-open Patent, the hydraulic pump motor 58 for revolution is driven by pressure oil supply from the accumulator 56, and therefore a hydraulic circuit including the pressure accumulation assisting means 55 (for example, an electric motor and a hydraulic pump), the control valve 57 and the accumulator 56, which makes a system complicated. Further, since part of energy generated by the engine 51 is recovered at the time of braking revolution, the engine output can be decreased more than the prior art, but since recovering amount of energy is not enough, the engine 51 cannot be made sufficiently compact.
The present invention is made in view of the above-described disadvantage, and its object is to provide hybrid construction equipment, which can make an engine compact by leveling a load exerted on the engine and efficiently regenerating energy with a simple system.
In order to attain the above-described object, hybrid construction equipment according to the present invention is hybrid construction equipment including, on an upper revolving superstructure rotatably placed on a lower traveling unit, an engine, a hydraulic pump driven by the engine, a hydraulic actuator driven by discharge oil from the hydraulic pump, a first electric motor driven by the engine, a battery for charging electric power generated by the first electric motor, and a second electric motor driven by electric power of the battery, and has the constitution in which
the second electric motor is the electric motor for revolving the upper revolving superstructure, which functions as a generator at a time of braking revolution of the upper revolving superstructure and charges generated electric power into the battery, and
the hybrid construction equipment further includes
absorption torque detecting means for detecting absorption torque of the hydraulic pump, and
a controller for comparing predetermined output torque of the engine, which is fixed according to an engine property, and absorption torque of the hydraulic pump detected by the absorption torque detecting means, controlling the first electric motor to function as a generator by surplus torque when the absorption torque of the hydraulic pump is smaller than the predetermined output torque of the engine, and controlling the first electric motor to function as a motor so that it generates an amount of shortage of torque when the absorption torque of the hydraulic pump is larger than the predetermined torque of the engine.
According to the above constitution, when the working load is small, and the absorption torque of the hydraulic pump is smaller than the predetermined output torque of the engine, the first electric motor is made to function as a generator and power is generated with a surplus amount of the engine output power and is charged into and stored in the battery. On the other hand, when the working load is large, and the absorption torque of the hydraulic pump is larger than the predetermined output torque of the engine, the first electric motor is made to function as a motor, and this is driven by the stored electric power to generate an amount of shortage of torque to assist the engine to drive the hydraulic pump. Specifically, the output power of the engine is used in such a manner as to xe2x80x9cstore a surplus when there is the surplus, and provides what is stored when it is insufficientxe2x80x9d, and therefore energy-saving and leveling of the load exerted on the engine can be achieved. As a result, the engine having the rated output power corresponding to the average required horsepower can be adopted while the absorption torque of the hydraulic pump is maintained.
Since the revolution driving system is electrically powered, it is possible to constitute the system of the revolution driving system by a simple system without a hydraulic device, inertia energy of the revolving superstructure can be converted into electric energy and regenerated at the time of braking revolution. By performing regeneration of the revolution, part of the engine output power is efficiently recovered. Since the energy regeneration is carried out, the above-described average required horsepower becomes lower, and the adopted engine can be made sufficiently compact.
Further, in the hybrid construction equipment,
the hydraulic actuator is a boom cylinder, and
the hybrid construction equipment may have the constitution further including
a hydraulic motor rotated by return oil from a bottom side of the boom cylinder, and
a generator connected to the hydraulic motor and charging generated electric power into the battery.
According to the above constitution, the system for generating power by using the high-pressure return oil from the boom cylinder is used, and thus the potential energy of the working machine can be converted into electric energy and regenerated. As a result that the regeneration at the time of lowering the boom is performed, the average required horsepower becomes lower than the first aspect of the invention, and therefore the engine can be made further compact.